I work at a large company that blocks all Internet ports, only allowing access to the web through a proxy server on ports 80 and 443. I have a fast connection at home and a nice shinny PowerBook sitting on my coffee table all alone. I searched high and low to find exactly how to accomplish this, but I could only find bit and parts.
I connect from Windows with ssh through the work proxy to my Airport Express then to my Mac. I tunnel a VNC connection through ssh, and control the desktop remotely. Make sure you are not violating your company's policies before attempting this.
My company forces me to use a Windows computer at work, but there are tools that will let you connect back home. I chose PuTTY (for Windows) for connecting via ssh to home. I configure PuTTY to go through the proxy, and to tunnel port 5900. I also set up a dyndns host to deal with the changing IP address of the home computer. I enabled remote login and Apple Remote Desktop (ARD) in the Sharing panel of System Preferences. After enabling ARD, click the Access Privileges button on its Sharing screen, select ‘VNC viewers may control screen with password,' and type in a password.
You will need to set up your Airport Express to forward ports 22 and 5900 to your PowerBook. Do this buy opening Airport Admin and selecting Port Mapping, press the Add button, and type public port 22 to the PowerBook's internal IP address (i.e. 10.0.1.2), and private port 22. Do the same for port 5900.
For work, I login with PuTTY via ssh and then I use TightVNC to control the desktop at home. I also found this link, which covers PuTTY tunnel configuration. Now you are on your way to setting up other home server services such as WeDAV, FTP Web etc.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20051102173302946